High-frequency oscillator



` July 11, 1939- J. F. FARRiNGToN 2,165,468

HIGH-FREQUENCY OSCILLATOR y Filed Feb. 16, 1937 INVENTOR. JOHN F. FARRINGTON ATTORNEY.

Patented July'll, 1939 PATENT OFFICE HIGH-FREQUENCY OSCILLA'OR John F. Farrington, Flushing, N. Y., assignor to Haxeltine Corporation, a corporation of Dela- Wale Application February 16, 1937, Serial No. 125,969 12 Claims. (Cl. Z50-36) This invention relates to high-frequency signaling systems, and more-particularly to improvements in tunable oscillation systems or coupling systems useful in such signaling systems.

Conventional high-frequency signaling systems generally comprise two or more tunable systems, such as oscillation .or coupling systems,

, having adjustable tuning elements ganged together for uncontrol operation, whereby the sys-- tems may be tuned over the same or different frequency ranges. In the case of a superheterodyne wave-signal receiver, one oscillation system is associated with a vacuum tube .to form a local beat-frequency oscillator, .the oscillation frequency being maintained at a fixed frequency difference with respect to that of the other tunable systems, such as the signal-selector systems, of'

the rceiver. The adjustable tuning elements of such systems are usually variable capacitance elements. However, as pointed out in the copending application of Harold A. Wheeler and John F. Farrington, Serial No. 125,968, filed Feb. 16, 1937, certain definite advantages are attendant upon inductance tuning of the selector and oscillator frequencydetermining circuits, particularly lwhen it is desired to tune over a wide range of frequencies. One of the important advantages concerns the resonance gain of such a system as determined by the anti-resonant impedance a0 thereof, it being possible to maintain a maximum anti-resonant impedance and, as a consequence, a lhigher resonance gain throughout the tuning range when inductance tuning is used.

In the aforementioned copending application, I

the advantages of inductance tuning of the various tunable circuits are realized by providing atunable system including an inductance tuning unit` of novel construction and arrangement. Briefly, the tuningunit comprises a winding and a nonmagnetic conductive shield relatively movable with respect to each other into and out of l coupling relationship and so related in configuration that there is procured the closest coupling therebetween consistent with the avoidance of 5 lfrictional. contact and excessive capacitance.

While this' form of tuning unit is particularly desirable for the application specified, it gives rise to certain additional problems, particularly in the construction of an oscillation or coupling .0 system having a satisfactory frequency-response characteristic. More specifically, difficulties arise in obtaining a transfer circuit between the input and output circuits of the system which will ensure an output voltage of substantially uniform u amplitude at all frequencies within the tuning range. These diillculties arise primarily in obtaining satisfactory coupling between the transfer circuit and the tunable frequency-determining circuit and, further, in compensating for the variations in the output voltage, particularly at 5 one end of the tuning range, occasioned by variations in the anti-resonant impedance of the frequency-determining circuit.

It is'an object of-the present invention, therefore, to provide an oscillation system,.tunable l0 over a wide frequency range by variable inductance means included in the frequency-determining circuit, which operates in a manner such that the frequency-response characteristic thereof is approximately uniform-at all frequencies withlnllS the range.

More specifically, it is an object of the invention to provide an oscillator including an oscillation system of the above general arrangement in which the effective coupling between the energy 20 transfer circuit and the frequency-determining circuit is independent of frequency and the characteristics of the transfer circuit are such as to compensate for tendencies toward output voltage variations occasioned by variations, with lfre- 25 quency, of the antiresonant impedance of the frequency-determining circuit.

In brief, the above objects are attained in accordance with the present invention by providing a tunable oscillation system comprising a pair 0f 30 input terminals, a pair of output terminals, a frequency-determiningv circuit connected to one of the pairs of terminals and including an adjustable inductance tuning unit, which may be of the type described briefly above and described in de- 35 tail and claimed in the copending application referred to above, and a transfer circuit inductively coupled to said frequency-determining circuit and connected to the other of said pairs of terminals. In the preferred embodiment, the trans- 4o fer circuit is coupled to a fixed inductance element, connected in parallel with the adjustable inductance tuning unit and, with suitable capacitance means, forming the frequency-determining circuit.` In order to compensate for tendencies 46 toward variations in output voltage with variations of theantiresonant impedance of the frequency-determining circuit, thetransfer circuit is so proportioned that its responsiveness varies with frequency, at the affected end of the tuning 50 range, in a sense to provide the. desired compensation. More'particularly, this circuit is designed to be resonant at a frequency in the vicinity of, but above the upper limit of the tuning range, so' that the tendency toward4 a decrease in 55 described, as that of the local oscillator, to opcrate at a fixed frequency difference with respect to one or more additional circuits tunable by similar adjustable inductance elements over a wide tuning range, the fixed inductance element in parallel with the tuning unit may also comprise a part of the aligning means, simulating the function of the conventional series-padding condenser used in capacitance tuned circuits.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as toits organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawing, in which Fig. 1 shows the application of the invention to a tunablecoupling stage, while Fig.2 illustrates the invention as applied to a local beat-frequency oscillator of a high-frequency signal-receiving system of the superheterodyne type.

Referring now more particularly to the drawing, Fig. 1 illustrates a tunable oscillation system embodying the invention utilized to couple an antenna circuit to the first vacuum tube amplifier of a high-frequency signal receiver, while Fig. 2 is a circuit diagram, partly schematic, of a receiver of the superheterodyne type having embodied therein a local oscillator constructed and arranged in accordance with the present invention. l Referring particularly to Fig. 1 of the drawing, there is shown a tunable oscillation system comprising input terminals I connected to an antenna-ground circuit and output terminals 2 coupled to the input circuit of a vacuum tube 8 through a high-frequency by-pass condenser 9, the output circuit of the tube 8 being coupled to a signal-translating system, which may comprise a conventional radio receiver. The oscillation system comprises a. frequency-determining circuit connected to the output terminals 2 and including an adjustable inductance element 5, which may be constructed and arranged in accordance with the invention of the aforesaid copendng application, connected in parallel with a fixed inductance element 'i and a condenser S, shown as a fixed condenser though in some cases it may also be variable. There is also provided a transfer circuit connected to the input terminals l and comprising an inductance element 3 coupled to the fixed inductance element 1 of the frequency-determining'circuit and having a condenser 4 connected in parallel therewith to A'tune the transfer circuit outside of, preferably above, the tuning range of the system. As indicated, a source of control bias may be connected to the grid of the tube 8 to control its amplification in a conventional manner.

The advantages of using an adjustable inductance unit to tune a tunable system :over a wide frequency range have been pointed out above. However, as was noted above, when this form of tuning is employed, certain difficulties, pertaining particularly to the coupling of the transfer circuit to the frequency-determining circuit and the variation in voltage across the latter circuit occasioned by variation in its antiresonant impedance, must be overcome if' the system is to have a fairly uniform output voltage over the entire tuning range. these difficulties, the impracticability of attempting to couple the inrluctance element 3 to the adjustable inductance element 5 to secure coupling therebetween, independent of any adjustment of the latter element, is readily apparent.

In accordance with the present invention, coupling between the transfer circuit 3, l and the frequency-determining circuit 5, t, i which is independent of frequency and the adjustment of the inductance element 5 is obtained by connecting the fixed inductance element ll in parallel with the other elements of the frequency-determining circuit and inductively coupling thereto the element 3 included in the transfer circuit, thus forming, in effect, a transformer. As is well known. the voltage transformation ratio of this form of transformer is independent of frequency lin regard to the first oi" so that the ratio of the voltage induced across the element 3 to that across the circuit 5, 6, is independent of frequency and it may be said that the effective coupling between the transfer circuit and the frequency-determining circuit is approximately constant over the tuning range.

lit is known that the losses in such a tunable system are such that the antiresonant impedance of the resonant circuit tends to decrease with increasing frequency, so that the voltage across the system tends to decrease with increasing irequency. In conventional arrangements this eifect is too small appreciably to reduce the voltage vacross the frequency-determining circuit. With the arrangement shown, however, the decrease in antiresonant impedance with frequency is exaggerated by the adjustment of the inductance thereof to increase the frequency of the system. As a result, the decrease in voltage across the output of the tunable system at the high-:frequency end of the tuning range becomes very considerable.

In accordance with the present invention, the problem outlined above is overcome by tuning the transfer circuit'comprising `the inductance element 3 and condenser 'l to resonance at a frequency in the vicinity of, but above,l the upper limit of the tuning range. As a result, the increase in the resonance gain of the transfer circuit compensates for the tendency of the voltage across the output circuit of the tunable system to decrease as the system is tuned to frequencies approaching the upper limit of the tuning range. In other words, the increase in resonance gain with frequency effectively increases the trans- Referring now to Fig. 2 of the drawing, there,

is shown a complete superheterodyne receiver having the present invention embodied in the oscillation system of the local beat-frequency' oscillator. While the receiver shown is described more particularly with reference to its use in. the reception of sound signal-modulated carrlers, it will be understood that it may be used for the reception of television signal-modulated carriers by modification of conventional elements thereof. Briefly described, the receiver comprises a tunable radio-frequency amplifier l0 having its input circuit coupled to an antenna-ground circuit Il and its-output circuit coupled to the input circuit of a tunable frequency changer the frequency changer i2. in the order named.

are an intermediate-frequency amplifier i2, ay 4detector and Asource of automatic amplification control bias i4, a signal-frequency amplifier il, and a translating device i4 indicated as a sound reproducer.

also coupled to the input circuit of the frequency changer |2,-.by means comprising a'condenser i1, is a local beat-frequency oscillator constructed and arranged in accordance with the present invention and indicated generally at I4. This oscillator comprises a shielded vacuum tube 2ii, preferablyv a pentode. having its input and output electrodes coupled to a tunable system 2i connected to terminals 2, corresponding to the terminals 2 of Fig. 1, though in this case they are connected as input terminals, being connected to the output electrodes4 of the tube 20. Preferably, the tube 2l is of a type having minimum inherent capacitance between its electrodes and lead-in wires. As indicated, adjustment of the resonant frequency of the system 2iA over the desired tuning range is accomplished by varying the inductance of an adjustable inductance 22, which may be constructed and arranged in accordance with the invention disclosed in the aforesaid application, 'connected in parallel with a fixed' inductance element 2l and fixed capacitance means 24. 'Ihe capacitance means 24 may comprise only the output capacitance of the tube 20 andthe stray lead capacitances, all effectively in series with the direct current blocking condenser 25. The energy transfer circuit coupled between the input electrodes of the tube 20 and the frequencydetermining circuit 2l comprises essentially the inductance element 24 coupled to the inductance element 23 and the capacitance l0 consisting of the grid-cathode capacitance of the tube 20 and stray lead capacitance. There is also connected in this circuita grid-leak resistor 21 which is shunted by a -high-frequency bypass condenser. 28. The transfer circuit is connected between the terminals i, corresponding to the terminals i of Fig. l, but in this case effectively constituting output terminals of the oscillation system.

Additional features of the circuit include the complete shielding of the elements of the oscillator i8, as indicated by the dashed line i9; the

application of voperating voltages of appropriate value to the screen and anode electrodes of the oscillator tube through the +B terminal and appropriate voltage dropping resistors; the connection of the tuning units of the several tunable circuits included in theA vamplifier i0, the frequency changer i2, and the oscillator Il for unicontrol adjustment, as indicated by the dotted line U; and the provision of an automatic ampliflcation control circuit including the connection 29 for deriving from the detector i4 a bias voltage variable with the signal-carrier amplitude and applying the same negatively tothe input electrodes of one or more of the tubes included in the radio-frequency amplifier ill and the intermediate-frequency amplifier i3 to maintain the signal ontput within a narrow range for av wide range of signal-input amplitudes.

The receiver, as generally described above. is of the conventional superheterodyne type, the

operation of which is well understood in the art. Briefly. -a desired signal-modulated carrier intercepted by the antenna circuit Il is selected and amplified in they radio-frequency amplifier i0, is further selected and converted into a modulated intermediate-frequency signal in the modulator or frequency changer i2, is further selected and amplied by the intermediate-frequency amplifier i2. and is supplied to the detector i4 for rectification. ponents are derived by the detector i4 and are amplied in the signal-frequency amplifier il and supplied to the translating device il for reproduction. The amplitude of the input voltage to the detector I4 ismaintained within narrow limits through the action of the automatic amv pliilcation control circuit in the manner well understood in the art.

The modulation-frequency comv vAs in the arrangement of Fig. 1, by coupling the inductance element 26 of the transfer circuit to the fixed inductance element 22 of the frequency-determining circuit there is procured an effective coupling to the oscillation circuit, tunable by an adjustable inductanceelement, which is substantially constant over the tuning range of the system, while, by tuning the transfer circuit 23, 2li above the upper limit of the tuning range, variations in the antiresonant impedance of the frequency-determining circuit 2i are approximately compensated, thereby imparting an approximately uniform output voltage characteristic to the oscillator i8 throughout its tuningy range.

As mentioned above.l an additional feature'of the invention concerns the useof the inductance element 23 as a portion of the aligning means for maintaining frequency alignment between the frequency-determining circuit 2i of the oscil lator i8 and the tunable systems embodied in the amplifier Iii and the frequency changer i2. Thus, the tunable input circuit of the amplifier i0 and the frequency-determining circuit 2i comprise a pair of circuits tunable to different frequencies and over different frequency ranges,

and it is conventional practice to align these circuits so that the frequency difference thereof 4is maintained approximately constant over their respective tuning ranges. This is usually accomplished in conventional arrangements employing variable capacitance tuning by using seriesand parallel-padding condensers in one or more of the circuits; In an arrangement of the form described. however, wherein inductance Atuning is employed, alignment may be securedby adjusting the inductances of the circuits. The inductance element 22 may conveniently be used for this purpose by properly proportioning the in-y ductance thereof relative to the inductance of the tunable circuits with which the circuit 2i is to be aligned and constructing `the element so that its inductance may be adjusted within suf, ilciently wide limits to permit alignment of this circuit with the other circuits. In the arrangement described, also the parallel capacitance is preferably given a value different .than that of the other tunable circuits with which the oscillator is to be aligned, by analogy to the use of the inductance elements of different inductance value in conventional variable capacitance tuning arrangements.

While it will be understood that the circuit specifications of the oscillator i8 may vary according to the design of any particular application, the following circuit specifications iorI an oscillator employed for the application described are included, by way of example only, using an acorn tube of the 954 type:

Rudio-frequency tuning range 58-100 megacyclos.

Condenser 25 .O02 microfarad.

Condenser 24 (total effective shunt 7 micro-microfarads.

capacitance ofthe circuit 21).

layer close wound on a cylindrical form 1%: inch diameter over a comminuted iron core. Maximum inductance 1.4 microhen manciano@ element 2s iertlsrhs No. 2c D. s. o. single layer close wound on l inch Bakelite rod. Inductanee 3.8 microhenries.

Inductanec element 2G 2% turns No. 26 D. S. C. single layer close wound on the same Bakelite rod as inductance element 23 with the adjacent low potential ends of the two elements spaced one turn apart,

The shield for varying the inductance of the element 22 comprises a brass member having a conically shaped inner surface relatively movable in telescoping relationship to the turns of this element.

While there have been described what are at present considered to be the preferred embodiments of the invention, it will be understood that various changes and modifications may be made therein without departing from the invention, and it is contemplated in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

. 1. A tunable coupling system comprising a pair of input terminals, a pair of output terminals, a frequency-determining circuit connected to one of said pairs of terminals including a pair of inductance elements and fixed capacitance means, all effectively in parallel, one of said inductance elements being adjustable to vary the frequency of said circuit continuously over a wide range, and a transfer circuit connected to the other of said pairs of terminals and including a third inductance element coupled to the other of said pair of inductance elements.

2. A tunable coupling system comprising a pair of input terminals, a pair of output terminals, a frequency-determining circuit connected to one of said pairs of terminals including a pair of inductance elements and fixed capacitance means, all effectively in parallel, one of said inductance elementsbeing adjustable to vary the frequency of said circuit continuously over a wide range, and a transfer circuit connected to the other of said pairs of terminals and including a third inductance elementl coupled to the other of said pair of inductance elements, said transfer circuit being resonant at a fixed frequency 'outside of said frequency range.

3. A tunable coupling system comprising a pair of input terminals, a pair of output terminals, a frequency-determining circuit connected to one of said pairs of terminals including a pair of inductance elements and fixed capacitance means, all effectively in parallel, one of said inductance elements being adustable to vary the frequency of said circuit continuously over a wide range, and a transfer circuit connected to the other of saidpairs of terminals and including a third inductance element coupled to the other of said pair of inductance elements, and capacitance effective to tune said third inductance element to a. frequency in the vicinity'of the highest frequency of said range.

4. An oscillator comprising a vacuum tube including input and output electrodes, a frequency-determining circuit coupled to one of said electrodes, said circuit including parallel-connected fixed capacitance means and at least one inductance element adjustable to vary the frequency of said circuit continuously over a wide range, said frequency variations incidentally varying the parallel :impedance of said circuit to an extent sufficient to vary the voltage across said circuit as the frequency of said circuit approaches one end of said range, and an energy transfer circuit coupled between the other of said electrodes and said frequency-determining circuit, the reactive constants of said transfer circuit being so proportioned that the responsiveness thereof varies with frequency atsaid one end of said range in a sense to compensate for the effect of said variation in voltage, thereby to render the output voltage of said oscillator more nearly uniform throughout said range.

5. An oscillator comprising a vacuum tube including input and output electrodes, a frequencydetermining circuit coupled to one of said electrodes, said circuit including parallel-connected fixed capacitance means and at least one inductance element adjustable to vary the frequency of said circuit continuously over a wide range, said frequency variations incidentally varying the parallel impedance of said circuit in a sense to decrease the voltage across said circuit as the frequency of said circuit approaches the highfrequency end of said range, and an energytransfer circuit coupled between the other of said electrodes and said frequency-determining circuit, the reactive constants of said transfer circuit being so proportioned that the responsiveness thereof increases as the frequency of said frequency-determining circuit approaches the high-frequency end of said range, thereby to render the output voltage of said oscillator more nearly uniform throughout said range.

6. An oscillator comprising a vacuum tubelncluding input and output electrodes, a frequencydetermining circuit coupled to said output electrodes, said circuit including parallel-connected fixed capacitance means and at least one inductance element adjustable to vary the frequency of said circuit continuously over a wide range, said frequency variations incidentally varying the losses in said circuit in a sense to decreasethe voltage across said circuit as the frequency of said circuit approaches` the highfrequency end of said range, and an energy transfer circuit coupled between said input electrodes and said frequency-determining circuit, the reactive constants of said transfer circuit being so proportioned that the responsiveness thereof increases as the frequency of said frequency-determining circuit approaches the highfrequency end of said range, thereby to render the output voltage of said oscillator more nearly uniform throughout said range.

7. An oscillator comprising a. vacuum tube including input and output electrodes, a frequencydetermining circuit coupled to one of said electrodes, said circuit including a pair of fixed inductance elements and capacitance means all effectively in parallel, one f said inductance elements being adjustable to vary the frequency of said circuit continuously over a wide range, and an energy transfer circuit coupled to the other of said electrodes and including a third inductance element coupled to the other of said pair of inductance elements.

8. An oscillator comprising a vacuum tube including input and output electrodes. a frequency- 11. An oscillator comprising a lvacuum tube in determining circuit coupled to one of said electrodes, said circuit including a pair of fixed inductance elements and capacitance means all ei'i'ectively in parallel, one of said inductance elements being adustable to vary the frequency of said circuit continuously over a wide range, and energy transfer means coupled to the other of said electrodes and including a third inductance element coupled tothe other of said pair of inductance elements tov provide an effectivel coupling between said frequency-determining circuit and said energy transfer means which is independent of the frequency of said circuit.

9. An oscillator comprising a vacuum tube including input and output electrodes, a frequencydetermining'circuit coupled to one of said electrodes, said circuit including a pair of inductance elements and fixed capacitance means all effectively in parallel, one of said inductance elements being adjustable to vary the frequency of saidv circuit continuously over a wide range, and an energy transfer circuit coupled to the other of said electrodes and including a third inductance cluding input and output electrodes, a frequencydetermining circuit coupled to one of said electrodes, said circuit including a pair of inductance elements and substantially fixed capacitance means all eectivelyl in parallel, one of said inductance elements being adjustable to vary the frequency of said circuit continuously over a wide range, said frequency variations incidentally varying the parallel impedance of said circuit in a sense to decrease the voltage across said circuit as the frequency of said circuit approaches the high-frequency end of said range, and an energy transfer circuit coupled to the other of said electrodes andlcomprising a third inductance element inductively coupled to the other inductance element of said pair and being resonant at a frequency above the high-frequency end of said range, the increased responsiveness thereof tending to compensate for the effect of s'aid variation in impedance of said frequency-determining circuit, whereby the output voltage of said oscillator is rendered more nearly uniform throughout said range.

cluding an input electrode, an output electrode, and a cathode, a frequency-determining circuit coupled to said cathode and said output electrode, y

said circuit including a pair of inductance ele-y ments and substantially fixed capacitance means all effectively in parallel, one. of said inductance elements being adjustable to vary the frequency of said circuit continuously over a wide range, said frequency variations incidentally varying the lossesA in said circuit in a sense to decrease the voltage across said circuit as the frequency of said circuit approaches the high-frequency end 'of said range. and an energy'transfer circuit coupled .to said cathode and said input electrode and including a third inductance element inductively coupled to the other of said pair of inductance elements and being resonant at a frequency above the high-frequency end of said range, the increased responsiveness thereof tending to compensate for the effect of said variation cuit elements and, connections, said inductance element being adjustable to vary the frequency of said circuit continuously over a wide range, said frequency variations incidentally varying the parallel impedance offsaid circuit to an extent suiiicie'nt to vary the voltage across said circuit as the frequency of said circuit approaches one end of said range, and an energy transfer circuit coupled between said input electrodes and said frequency-determining circuit, the reactive con-y stants of said. transfer circuit being so proportioned that the responsiveness thereof varies with frequency at said one end of said range in a sense -to compensate .for the effect of said variation in said parallel impedance, thereby to render the output voltage of said oscillator more nearly uniform throughout said range.

J'oms F. FARRINGTON;

CERTIEFICATE OF CORRECTION.

Patent No, 2,l65,h68. July ll, 1959.

- JOHN F; ymmm GToN.

It .is hereby certified that errer appears in the printed specificatior ofl the above numbered patent requiring, correction as follows: Page LL, second column, line 66, claim "f, strike out the word "fixed" and insert the same before "capacitance" in line 6?-, same laim; page 5, first column, line 5, claim 8, strike out the word "fixed" and insert the same before "capaci: tance" in line h., same claim; and that. thel eaid Lettera Patent should be read with this correction therein that the samema-y conferm to the recore ofthe case in the Patent Officeo signed and sealed wie ,29th day of August, A., D. 1959u l Leslie Frazer, (Seal) .listing Gommiesioner vof Patents. 

